A 3rd Generation Partnership Project (3GPP) proposes a concept of Licensed-Assisted Access (LAA) to use unlicensed spectrum with help of Long Term Evolution (LTE) licensed spectrum. Access technologies used on the unlicensed spectrum in related technologies, such as Wi-Fi, have weaker anti-interference capabilities. In order to avoid interference, many anti-interference rules have been designed in a Wi-Fi system. In an LTE network, since there is a good orthogonality which guarantees an interference level, it is not needed to consider in uplink and downlink transmission between a base station and a user whether there are other base stations or other users in a surrounding area which are transmitting data. If it is not considered whether other devices in the surrounding area are using an unlicensed frequency band when the LTE is used on the unlicensed frequency band, this will cause great interference to Wi-Fi devices. Since the LTE would transmit data once there is a service, and there is no monitoring rule, the Wi-Fi devices cannot transmit data when there is service transmission in the LTE and need to wait until the service transmission in the LTE is completed, and then can perform data transmission when a channel is detected in an idle state.
Traditionally, Physical Random Access Channel (PRACH) resource allocation of Time Division Duplexing (TDD) is as follows:
1. there are five formats of random access preamble sequences, i.e., preamble:
(1) format 0: occupy 1 ms;
(2) format 1: occupy 2 ms;
(3) format 2: occupy 2 ms;
(4) format 3: occupy 3 ms;
(5) format 4: occupies less than 1 ms and only occupies a Uplink Pilot Time Slot (UpPTS).
Detailed information of the above five formats is shown in Table 1:
TABLE 1Format of Random Access PreambleSequenceTCPTSEQ03168 · Ts24576 · Ts121024 · Ts 24576 · Ts26240 · Ts2 · 24576 · Ts321024 · Ts 2 · 24576 · Ts4 448 · Ts 4096 · Ts
2. Each PRACH occupies contiguous six Resource Blocks (RBs) in frequency and is located between a Physical Uplink Control Channel (PUCCH) and a Physical Uplink Shared Channel (PUSCH).
Meanwhile, in a conventional case, PRACH transmission does not require channel detection. However, in an LAA TDD system, since there is interference to other systems such as Wi-Fi systems, it needs to solve the technology problems whether a channel detection is necessary to perform before a User Equipment (UE) transmits the random access preamble sequences, and whether different channel detection mechanisms need to be used for different formats of the random access preamble sequences.